The production of blister copper to date has been dominated by use of Pierce-Smith converters. However these converters are progressively falling further behind environmentally acceptable standards for off-gas emissions. In more recent times, technologies such as those developed by Outokumpu and Mitsubishi have been adapted to the production of blister copper. These not only provide an improvement in environmental performance over the Pierce-Smith converters, but also improve the scale of operation and productivity. Still more recent is the proposal of Edwards et al disclosed in U.S. Pat. No. 5,888,270, issued 30 Mar. 1999.
The proposal of Edwards et al utilises what is referred to as a lance based process. More specifically, the process uses a top-submerged injection lancing furnace in which an injection lance is lowered from above a molten bath to submerge a discharge tip at its lower end for injection within the bath. The bath consists of a continuous slag phase, in particular of a calcium ferrite slag, which floats on a continuous molten blister copper phase. Matte and/or concentrate, together with a suitable flux, is added to the slag phase while that phase is agitated by the submerged injection of an oxidizing gas capable of reacting with the matte and/or concentrate to form blister copper. The lance tip is located deep within the slag phase to ensure that a substantial proportion of injected oxidizing gas contacts the blister copper phase.
It is suggested in Edwards et al that contact of oxidizing gas with the blister copper oxidises the blister copper and generates copper oxide which floats to an interface between the slag and blister copper phases. It is further suggested that the copper oxide reacts with matte or concentrate which reaches the interface, or alternatively is dissolved or dispersed in the slag to react with the matte or concentrate. It also is contended that the copper oxide assists desulphurisation of the copper and improves the utilization of oxygen by the sulphur with concomitant reduction of the sulphur content of the blister copper and of copper losses to the slag. However, low sulphur blister copper contents are said to be achieved by injecting oxygen directly into the copper layer, as distinct from merely deeply injecting the oxygen in the slag for contacting the copper layer at its interface with the slag layer.
The present invention also relates to a process for producing blister copper by top-submerged injection. However, the process of the invention is directed to a process which obviates the need for a substantial proportion of an oxidizing gas to make contact with the blister copper phase, or for any need for injection into the copper phase through its interface with the continuous slag phase.